However, the foundation also said the U.S. Internal Revenue Service is scrutinizing how the foundation treated the revenue it received from Google. Baker put it this way:

In 2005 the Mozilla Foundation established a "tax reserve fund" for a portion of the revenue the foundation received that year from Google. We did this in case the IRS decided to review the tax status of these funds. This turns out to have been beneficial, as the IRS has decided to review this issue and the Mozilla Foundation. We are early in the process and do not yet have a good feel for how long this will take or the overall scope of what will be involved.

Mozilla features Google prominently in two ways: a default start page with a Google search box, and a search bar in the upper right corner of the Firefox interface. Users can configure the search bar to use search from a variety of others, too. Baker said Yahoo and Amazon.com provided a smaller quantity of extra revenue, but Google accounted for 88 percent of the foundation's money.

In an interview, Baker said Mozilla is watching Chrome but isn't particularly worried. The search partnership is analogous to Google's AdSense program, in which Web sites show Google advertisements and share the resulting revenue with Google, and Google has many such partnerships. And, she added, "Our market share continues to grow, and we expect it to be healthy."